Get one of these bad oscars, some spandex, crank bros pedals, a full face helmet; then go rage on some abandon railroad trails.
I don't know much about the Iowa scene, but if you can find a place that rents bikes, they'll usually turn over their rentals once a year and you can get bikes that have been ridden <5 times for 1/2 price. I'd also see if they'll let you rent something and put that towards the purchase price.
If you start off clipped in you'll have some cool scars to look forward too, but chicks love scars so that's up to you. I personally hate camelbacks and only wear them on rides over 2 hours if self supported, but lots of friends wear them everywhere. I usually carry a water bottle, pump mounted to frame and a saddle bag (multi-tool, tire iron, and extra tube inside). My bike is a 29er and I've yet to pop a tire, which I think is fairly common as they're just beefier. If you're riding trails in the IA, I would think you'd be hard pressed to need that, but they're awesome.
If you're young, aggressive, and generally want to go big I would suggest dual suspension and disc brakes at a minimum. If that doesn't describe your projected riding style, feel free to skimp on those types of things.
You've made a good decision, hope you have fun.
